Rumored for what seems like months, the deal was held up for some time due to Newcastle's desire to have a replacement lined up before allowing Debuchy to move on. With the closure of the Magpies' purchase of Feyenoord's Daryl Janmaat (
which I think they still haven't announced! which they announced just after Arsenal's signing of Debuchy went through), that replacement is evidently in, and Debuchy is now free to go.
Debuchy was a key man for France in the just-ended World Cup, starting every game but their dead rubber final group match against Ecuador. He actually earned that starting spot ahead of the man whose Arsenal place he will be taking over, as Bacary Sagna was (for reasons that remain mysterious to me) mostly relegated to the bench for the tournament. Does that mean Arsenal are getting the better player? Of course not - anyone who's watched Arsenal for the last several years knows how crucial Sagna was. But it does mean that some concerns should be alleviated. Debuchy is no scrub.
Overall, to get a French international at a position of need for less than £15 million is pretty good business. He's not Alexis Sanchez, that's for sure, but this is a very good move for Arsenal. It's happy time.